Primary and secondary cases in Escherichia coli O157 outbreaks: a statistical analysis.

Hdl Handle:
http://hdl.handle.net/10147/94015
Title:
Primary and secondary cases in Escherichia coli O157 outbreaks: a statistical analysis.
Authors:
Snedeker, Kate G; Shaw, Darren J; Locking, Mary E; Prescott, Robin J
Affiliation:
Department of Population Medicine and Centre for Public Health and Zoonoses, Ontario Veterinary College, University of Guelph, Guelph, Ontario, N1G 2W1, Canada. snedeker@uoguelph.ca
Citation:
Primary and secondary cases in Escherichia coli O157 outbreaks: a statistical analysis. 2009, 9:144 BMC Infect. Dis.
Journal:
BMC infectious diseases
Issue Date:
2009
URI:
http://hdl.handle.net/10147/94015
DOI:
10.1186/1471-2334-9-144
PubMed ID:
19715594
Abstract:
BACKGROUND: Within outbreaks of Escherichia coli O157 (E. coli O157), at least 10-15% of cases are thought to have been acquired by secondary transmission. However, there has been little systematic quantification or characterisation of secondary outbreak cases worldwide. The aim of this study was to characterise secondary outbreak cases, estimate the overall proportion of outbreak cases that were the result of secondary transmission and to analyse the relationships between primary and secondary outbreak cases by mode of transmission, country and median age. METHODS: Published data was obtained from 90 confirmed Escherichia coli O157 outbreaks in Great Britain, Ireland, Scandinavia, Canada, the United States and Japan, and the outbreaks were described in terms of modes of primary and secondary transmission, country, case numbers and median case age. Outbreaks were tested for statistically significant differences in the number of ill, confirmed, primary and secondary cases (analysis of variance and Kruskal-Wallis) and in the rate of secondary cases between these variables (Generalised Linear Models). RESULTS: The outbreaks had a median of 13.5 confirmed cases, and mean proportion of 0.195 secondary cases. There were statistically significant differences in the numbers of ill, confirmed, primary and secondary cases between modes of primary transmission (p < 0.021), and in primary and secondary cases between median age categories (p < 0.039) and modes of secondary transmission (p < 0.001).Secondary case rates differed statistically significantly between modes of secondary and primary transmission and median age categories (all p < 0.001), but not between countries (p = 0.23). Statistically significantly higher rates of secondary transmission were found in outbreaks with a median age <6 years and those with secondary transmission via person to person spread in nurseries. No statistically significant interactions were found between country, mode of transmission and age category. CONCLUSION: Our analyses indicated that ~20% of E. coli O157 outbreak cases were the result of secondary spread, and that this spread is significantly influenced by age and modes of primary and secondary transmission, but not country. In particular, the results provide further data emphasising the importance of simple but effective preventive strategies, such as handwashing, that can reduce the risk of secondary spread, particularly amongst young children in nurseries.
Language:
en
MeSH:
Canada; Disease Outbreaks; Escherichia coli Infections; Escherichia coli O157; Great Britain; Humans; Ireland; Japan; Scandinavia; United States
ISSN:
1471-2334

Full metadata record

DC FieldValue Language
dc.contributor.authorSnedeker, Kate Gen
dc.contributor.authorShaw, Darren Jen
dc.contributor.authorLocking, Mary Een
dc.contributor.authorPrescott, Robin Jen
dc.date.accessioned2010-03-10T10:02:07Z-
dc.date.available2010-03-10T10:02:07Z-
dc.date.issued2009-
dc.identifier.citationPrimary and secondary cases in Escherichia coli O157 outbreaks: a statistical analysis. 2009, 9:144 BMC Infect. Dis.en
dc.identifier.issn1471-2334-
dc.identifier.pmid19715594-
dc.identifier.doi10.1186/1471-2334-9-144-
dc.identifier.urihttp://hdl.handle.net/10147/94015-
dc.description.abstractBACKGROUND: Within outbreaks of Escherichia coli O157 (E. coli O157), at least 10-15% of cases are thought to have been acquired by secondary transmission. However, there has been little systematic quantification or characterisation of secondary outbreak cases worldwide. The aim of this study was to characterise secondary outbreak cases, estimate the overall proportion of outbreak cases that were the result of secondary transmission and to analyse the relationships between primary and secondary outbreak cases by mode of transmission, country and median age. METHODS: Published data was obtained from 90 confirmed Escherichia coli O157 outbreaks in Great Britain, Ireland, Scandinavia, Canada, the United States and Japan, and the outbreaks were described in terms of modes of primary and secondary transmission, country, case numbers and median case age. Outbreaks were tested for statistically significant differences in the number of ill, confirmed, primary and secondary cases (analysis of variance and Kruskal-Wallis) and in the rate of secondary cases between these variables (Generalised Linear Models). RESULTS: The outbreaks had a median of 13.5 confirmed cases, and mean proportion of 0.195 secondary cases. There were statistically significant differences in the numbers of ill, confirmed, primary and secondary cases between modes of primary transmission (p < 0.021), and in primary and secondary cases between median age categories (p < 0.039) and modes of secondary transmission (p < 0.001).Secondary case rates differed statistically significantly between modes of secondary and primary transmission and median age categories (all p < 0.001), but not between countries (p = 0.23). Statistically significantly higher rates of secondary transmission were found in outbreaks with a median age <6 years and those with secondary transmission via person to person spread in nurseries. No statistically significant interactions were found between country, mode of transmission and age category. CONCLUSION: Our analyses indicated that ~20% of E. coli O157 outbreak cases were the result of secondary spread, and that this spread is significantly influenced by age and modes of primary and secondary transmission, but not country. In particular, the results provide further data emphasising the importance of simple but effective preventive strategies, such as handwashing, that can reduce the risk of secondary spread, particularly amongst young children in nurseries.-
dc.language.isoenen
dc.subject.meshCanada-
dc.subject.meshDisease Outbreaks-
dc.subject.meshEscherichia coli Infections-
dc.subject.meshEscherichia coli O157-
dc.subject.meshGreat Britain-
dc.subject.meshHumans-
dc.subject.meshIreland-
dc.subject.meshJapan-
dc.subject.meshScandinavia-
dc.subject.meshUnited States-
dc.titlePrimary and secondary cases in Escherichia coli O157 outbreaks: a statistical analysis.en
dc.contributor.departmentDepartment of Population Medicine and Centre for Public Health and Zoonoses, Ontario Veterinary College, University of Guelph, Guelph, Ontario, N1G 2W1, Canada. snedeker@uoguelph.caen
dc.identifier.journalBMC infectious diseasesen

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